Dual action inlet door and method for use thereof

ABSTRACT

An inlet door assembly and method for reducing noise from an auxiliary power unit (APU) contained within an aircraft housing is provided. The inlet assembly includes an inlet duct, an actuator, and a door. The inlet duct is configured to extend from the auxiliary power unit to the aircraft housing and has a sidewall that defines a flow passage through which APU noise propagates. The actuator is disposed at least partially within the inlet duct. The door coupled to the actuator. The actuator is also configured to selectively rotate the door between at least a first position, in which at least a portion of the door deflects APU noise in a first direction, and a second position, in which at least a portion of the door deflects the APU noise in a second direction.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/489,412, filed Jul. 22, 2003. This application is a divisional ofSer. No. 10/789,827 filed on Feb. 27, 2004.

FIELD OF THE INVENTION

The present invention relates to aircraft inlet doors, moreparticularly, inlet doors for use in the reduction of auxiliary powerunit noise.

BACKGROUND OF THE INVENTION

Auxiliary power units (“APU”) are used in aircrafts to provideelectrical power and compressed air to various parts of therein. When anaircraft is on the ground, its main source of electrical power comesfrom the APU. In particular, the APU can power the environmental controlsystems, air drive hydraulic pumps, and the starters for the engines.When an aircraft is in flight, the APU may provide pneumatic and/orelectric power to the aircraft.

Typically, APUs are located in the aft section of the aircraft, at ornear the tailcone section and include inlet and exhaust ducting thatexit through an opening in the aircraft fuselage to allow sufficient airflow through to the APU. For aircrafts on which APUs operate duringflight, a ram air door is typically provided to protect the APU fromforeign object damage when not in use and/or during ground movement, andto maximize airflow into the APU when performance at altitude isrequired. Thus, when APU venting is desired, the ram air door opens,either on the ground or in flight. Typically in such configuration, theram air door is configured to open around 45 degrees, relative to theaircraft fuselage, so that aircraft drag and entry of foreign objectsinto the inlet duct are minimized, while ram air recovery is optimized.

However, while the ram air door is open, noise may propagate from theAPU outward from the aircraft fuselage. The noise typically travelsthrough the inlet duct and is deflected from the interior of the ram airdoor to sections forward the tailcone or service locations that arelocated in the forward section of the aircraft. Because many aircraftsections are located forward of the APU, such as, for example, passengerdoors, passenger and aircraft personnel cabins, refueling points andbaggage doors, audible noise levels heard by those onboard the aircraftor those on the ground while handling baggage or performing aircraftmaintenance may be increased.

Therefore, there is a need for an air inlet door that does not enhanceforward propagation of inlet noise when the aircraft is on the ground.Moreover, in some cases, it is desirable for the inlet door to deflectforeign objects when the inlet door is open and while providing ram airrecovery in flight. Additionally, it would be beneficial for the inletdoor to cover the fuselage opening while the APU is not in operation.The present invention addresses one or more of these needs.

SUMMARY OF THE INVENTION

The present invention provides an inlet door assembly for reducing noisefrom an auxiliary power unit (APU) contained within an aircraft. Theinlet door assembly includes a duct and a door. The duct has an inletport, an outlet port, and a flow passage therebetween through which APUnoise propagates. The door is rotationally mounted on the duct andconfigured to selectively rotate between at least a first position, inwhich at least a portion of the door deflects the APU noise in a firstdirection, and a second position, in which at least a portion of thedoor deflects the APU noise in a second direction.

In one embodiment, and by way of example only, a method for reducing APUnoise from an APU located within an aircraft by an inlet door assemblyduring aircraft in-flight and ground operations is provided. An inletdoor assembly comprising a duct having an inlet port, an outlet port,and a flow passage therebetween through which APU noise propagates,forward and aft doors each rotationally mounted on the duct andconfigured to selectively rotate between at least a first position, inwhich at least a portion of the door deflects APU noise in a firstdirection, and a second position, in which at least a portion of thedoor deflects the APU noise in a second direction, is used. The methodincludes the steps of pivoting the aft door out of the flow passage andpivoting the forward door into the flow passage, during aircraftin-flight operation, pivoting the forward door out of the flow passage,while the aft door remains out of the flow passage, and pivoting the aftdoor into the flow passage, while the forward door remains out of theflow passage, during aircraft ground operation.

Other independent features and advantages of the preferred inlet doorassembly will become apparent from the following detailed description,taken in conjunction with the accompanying drawings which illustrate, byway of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional schematic showing an auxiliary power unit(APU) mounted in the tailcone of an airplane;

FIG. 2 is a perspective view of the inlet duct portion of an exemplarygas turbine APU 10;

FIGS. 3A-3C are perspective views of the APU inlet duct having anexemplary inlet door assembly mounted thereon;

FIGS. 4A-4C are schematics of the APU inlet duct having anotherexemplary inlet door assembly mounted thereon;

FIGS. 5A-5C are schematics of the APU inlet duct having anotherexemplary inlet door assembly mounted thereon

FIGS. 6A-6C are schematics of the APU inlet duct having yet anotherexemplary inlet door assembly mounted thereon;

FIGS. 7A-7E are schematics of the APU inlet duct having yet anotherexemplary inlet door assembly mounted thereon;

FIGS. 8A-8C are a schematics of the APU inlet duct having yet anotherexemplary inlet door assembly mounted thereon; and

FIGS. 9A-9C are perspective views of the APU inlet duct having yetanother exemplary inlet door assembly mounted thereon.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Before proceeding with a detailed description of the variousembodiments, it is to be appreciated that the air inlet assembliesdescribed below may be used in conjunction with various types of gasturbine engines, such as an aircraft turbofan jet engine, and varioustypes of aircrafts, watercrafts and ground-based installations. Theskilled artisan will appreciate that, although the present invention is,for convenience of explanation, depicted and described as beingimplemented in the context of an auxiliary power unit, it will beappreciated that it can be implemented with other sections of an engineas well. Additionally, as used herein, like numerals refer to likeparts.

Turning now to the description and with reference first to FIG. 1, across-sectional schematic of an auxiliary power unit (APU) 10 is shownmounted in the tailcone of an aircraft. The aircraft 14 includes acompartment 12 that is defined by the aircraft exterior surfaces 16 anda firewall 18. The exterior surface 16 includes an intake opening 20that communicates with the APU 10 via an inlet duct 21 (shown in FIG.2). Although the inlet duct 21 and intake opening 20 are shownpositioned on the underside of the aircraft, it will be appreciated thatboth may be located anywhere on the aircraft depending on the aircraftconfiguration. The firewall 18 separates the compartment 12 from therest of the aircraft fuselage. The APU 10 is disposed within thecompartment 12.

With reference to FIG. 2, the duct 21 includes an inlet port 35, anoutlet port 37, and a sidewall 38 that defines a flow passage 40 throughwhich the air passes and an inlet door assembly 42 that is mountedthereon. The amount of air that is ingested is controlled by the inletdoor assembly 42. The inlet door assembly 42 also controls the amount ofnoise that propagates from the APU 10 to the ambient environment.

Referring now to FIG. 3A for general reference only, an exemplary inletdoor assembly 42 is depicted. The inlet door assembly 42 generallyincludes a door 44 coupled to an actuator 46. The door 44 preferablyincludes first and second sides or ends 48, 50 and a seal 53 that isconfigured to sealingly couple the door 44 to the inlet opening 20 whenthe door 44 is in a closed position. The door 44 is rotationally mountedto the duct 21, and can be mounted to the duct sidewall 38, outlet port35, or may be mounted to the aircraft 16, such that at least a portionof the door 44 is rotatable between at least two positions, for example,into and out of the inlet duct flow passage 40. To this end, any portionof the door 44 may be rotationally coupled to the inlet duct 21. In onepreferred embodiment, the midsection of the door 44 is rotationallycoupled to the duct 21 so that when the door 44 is rotated in onedirection, the door first end 48 is rotated into the inlet duct flowpassage 40, and the door second end 50 is rotated out of the inlet ductflow passage 30, and vice versa when the door 44 is rotated in the otherdirection. In yet another embodiment, either the door first or secondend 48, 50 is mounted to the duct 21. In such an embodiment, the otherdoor end can rotate into and out of the inlet duct flow passage 40. Inan alternative embodiment, the door 44 may be coupled only to theactuator 46.

The actuator 46 is configured to move the door 44 between a firstposition, in which at least a portion of the door 44 deflects the APUair flow in a first direction, and a second position, in which at leasta portion of the door 44 deflects the air flow in a second direction.Alternatively, the actuator 46 is configured to move at least a portionof the door 44 into and out of the inlet duct flow passage 40. In yetanother alternative embodiment, the actuator 46 is configured to firstraise the door 44 away from the aircraft surface 16 and then rotate thedoor 44. Different types of actuators may be used depending on the inletdoor assembly configuration. For instance, the actuator 46 can be alinear or rotary actuator, but may be one of numerous other types ofmechanisms configured to actuate a door, including but not limited topiston assemblies, rack and pinion gear assemblies, multi-componentlinkages, and springs.

Turning now to FIGS. 3A-3C, in the embodiment depicted therein, theinlet door assembly 42 includes a door 44 having first and second sides48, 50, and a pair of arms 52 that each includes an opening 54 locatedproximate the door second side 50 that receives a coupling mechanism 56,such as a screw, or other type of mechanism configured to rotationallycouple the door 44 to the actuator 46. The actuator 46 includes amounting surface 58, to which the door 44 is coupled, and is incommunication, either electrically, pneumatically, or hydraulically,with a control circuit, an electronic control unit (ECU), or any one ofnumerous other types of control mechanisms (not shown) that communicatesdoor 44 position commands to the actuator 46. The actuator 46 is furthermounted to the inlet duct 21, or alternatively, the sidewall 38, or tothe aircraft 16, and is configured to cause the door first side 48 torotate into and out of the inlet duct flow passage 40. The door firstside 48 preferably rotates between −90 degress and +90 degrees, relativeto the aircraft surface 16 so that sufficient ambient air is allowedinto the inlet duct flow passage 40 when desired, while APU noise isreduced.

FIG. 3A illustrates the door 44 of the inlet door assembly 42 in aninward open position. The inward open position is used while theaircraft is on the ground and allows noise to propagate directly out ofthe inlet duct 21 minimizing deflection forward 90 the aircraft. Whenthe inward open position is desired, the control circuit (not shown)communicates the desired position to the actuator 54, which thenactuates the door 44 to a desired angle 62 causing the door second side50 to actuate inward while the aircraft relative to the aircraft surface16 and specifically, into the inlet duct 21. Thus, when the noise exitsthe inlet duct 21, it partially deflects off of the inner surface of thedoor 44 and bounces back into the inlet duct flow passage 40.Additionally, when the aircraft is taxiing on the ground, the outersurface of the door 44 acts a shield to deflect foreign objects from theinlet duct 21 and prevent damage thereto.

When the APU is not operating, such as during portions of flight, theinlet duct 21 is closed, as shown in FIG. 31B. The door 44 is preferablyin a closed position to lower aircraft drag. When the door 44 isactuated from the inward position shown in FIG. 3A, the control circuit(not shown) communicates to the actuator 46 to close the door 44 bycausing the door first side 48 to rotate until the door 44 is flushagainst the aircraft surface 16. Most preferably, the door 44 and theinlet duct 21 sealingly couple to one another so that foreign objects donot enter into the inlet duct 21 to damage the APU.

During flight, it may be desirable to open the door 44 outward, such asshown in FIG. 3C. The outward position is used to achieve ram airrecovery while minimizing aircraft drag when the aircraft is in flight.As with the other two positions, the control circuit (not shown)communicates the desired outward position to the actuator 46. Inresponse, the actuator 46 causes the door 44 to actuate so that the doorfirst side 48 rotates until it extends outward at a desired angle 64,relative to the aircraft surface 16. During flight, APU noise is not asmuch of an issue and thus, in this embodiment, will be partiallydeflected forward the aircraft 90. As may be appreciated, the door 44may be opened to any angle so as to maximize ram air recovery.

As will be appreciated, the door 44 may also be actuated from the closedposition in FIG. 3B to the open position shown in FIG. 3A, or from theopen position in FIG. 3C to the closed position of FIG. 3B.Additionally, the door 44 may also be actuated from the position shownin FIG. 3A directly to the position of FIG. 3C, via the position in FIG.4B.

FIGS. 4A-4C illustrate another exemplary inlet door assembly 42 that canbe used on the inlet duct 21 of an APU 10. In this embodiment, the inletassembly 42 includes a door 44. The door 44 includes a first, or “aft”side 48 and a second, or “forward” side 50. The door 44 is coupled tothe inlet duct 21 at its midsection, such that the aft and forward sides48, 50 pivot into and out of the inlet duct flow passage 40. The door 44is actuated by an actuator (not shown) that is coupled to the doormidsection. The actuator communicates with a control circuit (not shown)and is configured to receive door position commands from the controlcircuit to cause the door 44 to rotate. The actuator is furtherconfigured to rotate the door 44 in several positions. For instance, theactuator can be configured to cause the aft side 48 to pivot out of theinlet duct flow passage 40 causing the forward side 50 to pivot into theinlet duct flow passage 40 as shown in FIG. 4A. This configuration isused so that the outer surface of the door 44 acts as a shield todeflect unwanted objects from the inlet duct, while also deflecting theAPU noise in the directions of the flow passage 40 or aft the aircraft92. The actuator can also be configured to cause the aft side 48 topivot into the inlet duct flow passage 40 while the forward side 50pivots out of the inlet duct flow passage 40 for aircraft in-flightoperation, as shown in FIG. 4C. Here, the door 44 scoops and directs theambient air into the flow passage 40, while deflecting the APU noiseforward 90 and into the flow passage 40. Additionally, the actuator 46can be configured to cause the door 44 to lay flush with the aircraftsurface 16 when the APU is not in operation, illustrated in FIG. 4B.

FIGS. 5A-5C illustrate a variation of the exemplary inlet door assembly42 provided in FIGS. 4A-4C. In the embodiment depicted in FIGS. 5A-5C,the inlet door assembly 42 includes a door 44 and an actuating mechanism70. The door 44 is a single structure configured to sealingly couple tothe inlet duct 21 when in the closed position. The door 44 also includesa first, or “aft” side 48 and a second, or “forward” side 50 and amounting surface 72 coupled to and located on the underside thereof. Themounting surface 72 couples to the actuating mechanism 70 so that whenthe door 44 pivots, either the aft or forward side 48, 50 can contactthe inlet duct 21. The actuating mechanism 70 includes a pair of arms 76that each have first and second ends 80, 84. The first ends 80 arecoupled to the door mounting surface 72. The mounting surface 72 and armfirst ends 80 are each configured to operate with one another to allowthe door 44 to pivot on top of the arm first ends 80. The arm secondends 84 are each coupled to an actuator (not shown) and the door forwardside 50. As will be appreciated, the arm second ends 84 mayalternatively be coupled to the door aft side 48.

The actuators can be any one of numerous types of actuators that may beconfigured to move the arms 76 to thereby cause the arms 76 to actuate,and as a result, to pivot the door 44. Alternatively, the actuators canincorporate a piston mechanism located below the mounting surface 72that is configured to raise and lower the door 44 relative to theaircraft surface (not shown), and another type of mechanism configuredto cause the door 44 to pivot atop the arm second ends 84. In yetanother alternative, the actuator can incorporate a rack and pinionarrangement configured to raise and lower the door 44. The actuators arepreferably coupled to the inlet duct 21 but, as will be appreciated, theactuators may be coupled to or mounted on any portion of the inlet doorassembly 42. The actuators are preferably in communication with acontrol circuit, electronic control unit or any other type of controller(not shown) configured to communicate door position commands to theactuators 46.

When the aircraft is not in flight, the door 44 is preferably in aclosed position and sealingly coupled to the inlet duct 21. However, ifthe APU is in operation, the door 44 is preferably in a raised position,shown in FIG. 5A. In such case, the control circuit (not shown)communicates the desired position commands to the actuator to cause thedoor 44 to lift away from the aircraft surface. The actuator causes thearm 76 to actuate out of the inlet duct flow passage 40.

During ground operation, it may be desirable for the door 44 to be openaft 92, as shown in FIG. 5B. The control circuit (not shown)communicates the desired position to the actuator which causes the door44 to pivot on top of the arm second end 84 so that the door aft side 48contacts the inlet duct 21 while the door forward side 50 is opened outof the flow passage 40. Meanwhile, the arm 76 itself remains fixed inthe open door position depicted previously in FIG. 5A so that the door44 continues to be lifted away from the aircraft surface 16. This aftopen configuration allows ambient air to enter into the inlet duct 21while deflecting noise aft 92. Such configuration is desirable when theAPU is in operation and the aircraft is taxiing on the ground. The door44 acts as a shield to prevent foreign objects from entering into theinlet duct 21 and damaging the APU.

The door 44 can also open forward 90, such as shown in FIG. 5C. Theforward open door configuration is desirable when the aircraft is inflight and maximum ram air recovery is desired. To this end, the controlcircuit (not shown) communicates the desired position to the actuatorwhich causes the door 44 to pivot on top of the arm second end 84 sothat the door aft side 48 is out of the inlet duct flow passage 40 whilethe door forward side 50 contacts the inlet duct 21. Meanwhile, the arm76 itself remains fixed in the open door position depicted previously inFIG. 5A so that the door 44 continues to be lifted away from theaircraft surface 16. Thus, the door 44 acts as a scoop to receiveambient air into the inlet duct 21.

One of many advantages to the configurations depicted in FIGS. 5A-5C isthat the APU can be in operation at any time during flight or on theground, the reason being that the door 44 can remain in an openposition, as shown in FIG. 5A, during the transition between the aft andforward positions, shown in FIGS. 5B and 5C.

FIGS. 6A-6C schematically illustrates yet another variation of theexemplary inlet door assembly 42 shown in FIGS. 4A-4C. Here, the inletdoor assembly 42 includes a door 44 and an actuating mechanism 70. Thedoor 44 also includes a first, or “aft” side 48 and a second, or“forward” side 50 and a mounting surface 72 coupled to and located onthe underside thereof. The mounting surface 72 couples to the actuatingmechanism 70 so that when the door 44 pivots either aft or forward side48, 50 can contact the inlet duct 21. The actuating mechanism 70includes two arms 76, 78, each having a first ends 80, 82 that couple tothe door mounting surface 12. The mounting surface 72 and arm first ends80, 82 are each configured to operate with one another to allow the door44 to pivot on top of the arm first ends 80, 82. To this end, each arm76, 78 has a second end 84, 86. The first arm second end 84 couples toone actuator 46, while the second arm second end 86 includes anextension portion 94 that is coupled to a second actuator 47.

The actuators 46, 47 can be any one of numerous types of actuators thatcan be configured to move the arms 76, 78 to thereby cause the arms 76,78 to actuate, and as a result, to pivot the door 44. Alternatively, oneof the actuator can be a piston mechanism located below the mountingsurface 72 that is configured to raise and lower the door 44 relative tothe aircraft surface 16, while the other actuator is configured to causethe door 44 to pivot atop the second arm second end 86. In yet anotheralternative, the first actuator can be a rack and pinion arrangementconfigured to raise and lower the door 44. Each actuator 46, 47 ispreferably coupled to the inlet duct 21 but, as will be appreciated, theactuators 46, 47 may be coupled to or mounted on any portion of theinlet door assembly 42. The actuators 46, 47 is preferably incommunication with a control circuit, electronic control unit or anyother type of controller (not shown) configured to communicate doorposition commands to the actuators 46, 47.

When the aircraft is not in flight, the door 44 is preferably in aclosed position and sealingly coupled to the inlet duct 21. This isillustrated in phantom in FIG. 6A. However, if the APU is in operation,the door 44 is preferably in a raised position, also shown in FIG. 6A.In such case, the control circuit (not shown) communicates the desiredposition commands to the first actuator 46 causes the arm 76 to actuatepartially out of the inlet duct flow passage 40. As a result, the secondarm 78 actuates partially out of the inlet duct flow passage 40 as well,the extension portion 94 extends to compensate for the second arm 78outward movement, and the door 44 is lifted and positioned out of theinlet duct flow passage 40.

During ground operation, it may be desirable for the door 44 to be openaft 92, as shown in FIG. 6B. The control circuit (not shown)communicates the desired position to the second actuator 47 which causesthe extension portion 94 to pivot the door 44 on top of the arm secondends 84, 86 so that the door forward side 50 contacts the inlet duct 21while the door aft side 48 is opened out of the flow passage 40.Meanwhile, the first arm 76 itself remains fixed in the open doorposition depicted previously in FIG. 6A so that the door 44 continues tobe lifted away from the aircraft surface 16. This aft open configurationallows ambient air to enter into the inlet duct 21 while deflectingnoise aft 92. Such configuration is desirable when the APU is inoperation and the aircraft is taxiing on the ground. The door 44 acts asa shield to prevent foreign objects from entering into the inlet duct 21and damaging the APU.

The door 44 can also open forward 90, such as shown in FIG. 6C. Theforward open door configuration is desirable when the aircraft is inflight and maximum ram air recovery is desired. To this end, the controlcircuit (not shown) communicates the desired position to the secondactuator 47 which causes the extension portion 94 to pivot the door 44on top of the arm second ends 84, 86 so that the door forward side 50 isout of the inlet duct flow passage 40 while the door aft side 48contacts the inlet duct 21. Meanwhile, the first arm 76 remains fixed inthe open door position depicted previously in FIG. 6A so that the door44 continues to be lifted away from the aircraft surface 16. Thus, thedoor 44 acts as a scoop to receive ambient air into the inlet duct 21.

Yet another embodiment of the exemplary inlet door assembly 42 isschematically illustrated in FIGS. 7A-7E. In this configuration, theinlet duct 21 includes a well 96 that is proximate the inlet opening 20.The well 96 includes a sidewall 97 and a shelf 98. The inlet doorassembly 42 includes two doors 44, 55 that are each rotationally mountedat one side to the inlet duct 21 and coupled to the actuators 46, 47.The doors 44, 55 are configured to rotate at the coupling point and openside to side, relative to the aircraft body. The first door 44 isconfigured to rotate into and out of the inlet duct flow passage 40, orproximate and away from the well sidewall 97. The second door 55 isconfigured to rotate into or out of the inlet duct flow passage 40 aswell, but specifically close to and away from the well shelf 98. Asshown in the figures, it is preferable that the first door 44 is shorterin length than the second door 55 in accordance with this particularembodiment, however, it will be appreciated that the doors 44, 55 may beeither equal in length, or the second door 55 may be shorter than thefirst door 44, depending on the configuration of the inlet duct well 96.

The actuating mechanisms 46, 47 are coupled to the inlet duct sidewall38 and to each of the doors 44, 55. Any one of numerous other types ofactuators may be used that can be configured to cause the doors 44, 55to actuate. Each actuator 46, 47 is preferably coupled to or embedded insome portion of the inlet duct 21 but, as will be appreciated, theactuators 46, 47 may be coupled to or mounted on any portion of theinlet door assembly 42. The actuators, 46, 47 are preferably incommunication with a control circuit, electronic control unit or anyother type of controller (not shown) configured to communicate doorposition commands to the actuator 46, 47.

FIGS. 7A-7E illustrate the preferred sequence of operation to achievethe door positions shown in FIG. 7A-7C. When the APU is not inoperation, the doors 44, 55 are in a closed position, as shown in FIG.7A. When the aircraft is in flight, the control circuit communicatesposition commands to the actuators 46, 47 to cause the first actuator 46to rotate the first door 44 to an open out position where the first door44 opens out away from the inlet duct flow passage 40, while the secondactuator 47 rotates the second door 55 to an inward position into theinlet duct flow passage 40 proximate the well shelf 98. Thus, when theaircraft is in flight, air is scooped and directed into the inlet ductflow passage 40 via the first door 44. If the aircraft is taxiing on therunway, the control circuit (not shown) communicates new positioncommands to the actuators 46, 47. First, the control circuit (not shown)instructs the first actuator 46 to remain idle so that the first door 44remains out of the flow passage 40. Meanwhile, the control circuit (notshown) also causes the second actuator 47 to rotate the second door 55out of the flow passage 40, illustrated in FIG. 7C. After moving throughthe position shown in FIG. 7C, the first actuator 46 then rotates thefirst door 44 into the flow passage 40 proximate the well sidewall 152,while the second actuator 47 remains idle and the second door 55 remainsin the open outward position, shown in FIG. 7D.

During in flight APU operation, the control circuit (not shown) can sendposition commands to the actuators 46, 47 to rotate both doors 44, 55inward to maximize ram air recovery, as shown in FIG. 7E. This positionmay be achieved from the positions depicted in either FIG. 7B or 7D.From the position in FIG. 7B, the control circuit (not shown) causes thefirst actuator 46 to rotate the first door 44 into the inlet duct flowpassage 40 so that it is proximate the well sidewall 97. At the sametime, the second actuator 47 remains idle. Thus, the second door 55remains proximate the well shelf 98.

From the position in FIG. 7D, the control circuit (not shown) causes thefirst actuator 46 to remain idle so that the first door 44 remains inthe flow passage 40 proximate the well sidewall 97. Meanwhile, thesecond actuator 47 receives commands from the control circuit (notshown) to rotate the second door 55 inward so that it is proximate thewell shelf 98. The position depicted in FIG. 7E is desirable forin-flight low drag operation after the ram air recovery has beeninitiated.

FIGS. 8A-8C illustrate another exemplary inlet door assembly 42 similarto the embodiment shown in FIGS. 7A-7E. However, in this embodiment, thetwo doors 44, 55 are coupled to the inlet duct 21 and to an actuatingmechanism 70, wherein the two doors 44, 55 open the inlet duct 21 eitherforward 90 or aft 92. The actuating mechanism 70 further includes twojoining rods 64, 66 a linking rod 68 and an actuator 46. The joiningrods 64, 66 each have a first and a second end 72, 74. Each of the firstends 72 are fixedly coupled to the two doors 44, 55 preferably, on oneof the sides of each of the doors 44, 55 so that the ends 72, 74 anddoors 44, 55 are coupled at about a 90 degree angle. However, as will beappreciated, the two may be coupled together at any other position onthe doors 44, 55 such as to allow each door 44, 55 to rotate into andout of the inlet duct flow passage 40.

Preferably, when the rod second ends 74 are rotated, the doors 44, 55swing upward or downward, i.e. out of or into the inlet duct flowpassage 40. The second ends 74 are each coupled to the ends of thelinking rod 68 so that when the first door joining rod 64 is actuated tocause the first door 44 to move into a position, the second door joiningrod 66 also actuates, but causes the second door 55 to actuate into anopposite position. For example, if the first door 44 is actuated out ofthe flow passage 40, the second door 55 will, as a result, actuate intothe flow passage 40.

The actuator 46 is mounted within the inlet duct 21 and is coupled tothe linking rod 68. The actuator 46 can be any one of numerous types ofactuators that can be configured to move either the joining or linkingrods 64, 66, 68 to thereby cause the doors 44, 55 to actuate.Additionally, although depicted in the figure as coupling to one of thejoining rods 64, 66, as will be appreciated, the actuator 46 may becoupled to any portion of the actuating mechanism 70. Moreover, althoughthe assembly 42 is shown to include rods 64, 66, 68 that are used toactuate the two doors 44, 55, any other actuating mechanism, thatachieves the same result may be employed. The actuator 46 is preferablyin communication with a control circuit, electronic control unit or anyother type of controller (not shown) configured to communicate doorposition commands to the actuator 46.

Turning to FIG. 8A, an illustration of the inlet door assembly 42 duringground operation is provided. The actuator 46 receives position commandsfrom the controller (not shown). In this embodiment, the actuator 46pulls the second door joining rod 66 aft 92 causing the second door 55to rotate into the flow passage 40. Consequently, the linking rod 68 iscaused to pull on the first door joining rod 64 such that it alsorotates and moves aft the aircraft 92. The first door 44 moves out ofthe flow passage 40 into an open position. Noise propagates out of theinlet duct 21 with minimal deflection forward the aircraft 90.Specifically, the noise either is reflected off 94 of the inner surfaceof second door 55 and back into the inlet duct 21 or deflected off 96 ofthe inner surface of the first door 44 and back towards the aft sectionof the aircraft 92. Thus, the noise is reflected aft away from aircraftservice locations forward of the APU installation while sufficient ramair enters the inlet duct flow passage 40.

The door 44 is preferably in a closed position, such as shown in FIG.8B, while the APU is not in operation. When the doors 44, 55 areactuated from the position shown in FIG. 8A, the control circuit (notshown) communicates to the actuator 46 to close the door 44, 55 bypushing the second door joining rod 66 forward 90 and causing the seconddoor 55 to rotate upwards so that it is level with the aircraft surface16. Accordingly, the linking rod 68 causes the first door joining rod 64to rotate forward 90 so that the first door 44 consequently rotatesdownward until the first door 44 is level with the aircraft surface 16.Most preferably, the doors 44, 55 are configured to sealingly couplewith one another to seal the inlet duct 21 from foreign objects when inclose position.

During flight, APU noise is not as much of a concern. However, it isdesirable to allow sufficient ambient air into the inlet duct 21 for APUoperation, achieved by the door positions shown in FIG. 8C. If openingthe doors 44, 55 from the closed position shown in FIG. 8B, the controlcircuit (not shown) communicates the desired outward position to theactuator 46. In response, the actuator 46 pushes the second door joiningrod 66 forward 90 causing the second door 55 to rotate out of the flowpassage 40. This movement also causes the linking rod 68 to push thefirst door joining rod 64 forward 90 to cause the first door 44 toactuate into the flow passage 40. Thus, when the aircraft is in flight,the second door 55 scoops the oncoming air flow and directs the air 100into the inlet duct 21 for APU operation.

As will be appreciated by those of skill in the art, the control circuit(not shown) can be configured to cause the doors 44, 55 to actuate fromthe closed position shown in FIG. 8B to the open position shown in FIG.8A, or from the open position shown in FIG. 8C to the closed positionshown in FIG. 8B.

Yet another embodiment of the exemplary inlet door assembly 42 isillustrated in FIGS. 9A-9C. In this configuration, the inlet doorassembly 42 includes a main door 44 and a second door 55. The main door44 is rotationally mounted at its aft side to the inlet duct 21 andcoupled to the actuator 46. The main door 44 is configured to rotateinto and out of the inlet duct flow passage 40, or proximate and awayfrom the well sidewall 97. The second door 55 is coupled to the forwardside of the main door 44. The second door 55 is configured to extendaway from the main door 44 to contact the opposite side of the inletduct sidewall 38 to create a “tent” configuration. As shown in thefigures, it is preferable that the first door 44 is longer in lengththan the second door 55 in accordance with this particular embodiment,however, it will be appreciated that the doors 44, 55 may be eitherequal in length, or the second door 55 may be shorter than the firstdoor 44, depending on the configuration of the inlet duct well 96.

The doors 44, 55 can be rotated into several different positionsdepending on which phase of flight the aircraft is in. FIG. 9Aillustrates the inlet door assembly 42 in a closed position. The inletduct 21 is preferably kept closed when the APU (not shown) is not inoperation. When the aircraft is in flight, the APU is in operation, andram air recovery is desired, the doors 44, 55 may be in one of severalopen configuration. In one open configuration, such as shown in FIG. 9B,the main door 44 is open outwards from the aircraft surface 16 while thesecond door 55 is not extended and remains flush with the main door 44.This configuration allows ram air to be scooped into the inlet duct 21.Because noise is not a main issue during flight, noise that propagatesfrom the APU can deflect in any direction. In this configuration, thenoise is deflected forward the aircraft 90 and to the sides. In anotheropen configuration, shown in FIG. 9C, the second door 55 extends awayfrom the aircraft surface 16 to make a “tent” shape. Ambient air is ableto travel into the inlet duct 21, while APU noise is deflected sidewaysfrom the open doors 44, 55.

Thus, an improved inlet door assembly has been provided that isconfigured to achieve multi-positions to meet the requirements of ramair recovery, low ground noise, in-flight low drag, and foreign objectdamage. The invention also increases the duration for which an APU mayoperate by allowing the inlet duct 38 to remain open betweentransitioning between various door open positions. The improved inletassembly is also low in cost to implement.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt to a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodiment disclosedas the best mode contemplated for carrying out this invention, but thatthe invention will include all embodiments falling within the scope ofthe appended claims.

1. An inlet door assembly for reducing noise from an auxiliary powerunit (APU) contained within an aircraft having an aft end, the inletassembly comprising: a duct having an inlet port, an outlet port, and aflow passage therebetween through which APU noise propagates; a firstdoor rotationally mounted on the duct and configured to selectivelyrotate between at least a first position, in which at least a portion ofthe door deflects the APU noise in a first direction toward the aircraftaft end, and a second position, in which at least a portion of the doordeflects the APU noise in a second direction into the duct flow passage;a second door rotationally mounted on the duct proximate the first doorand configured to selectively rotate between at least a third position,in which at least a portion of the door deflects the APU noise in afirst direction, and a fourth position, in which at least a portion ofthe door deflects the APU noise in a second direction; and an actuatorcoupled to the first and second doors and configured to rotate the firstdoor to at least the first and second positions and to rotate the seconddoor to at least the third and fourth positions.
 2. The inlet doorassembly of claim 1, wherein at least a portion of the second door isdisposed within the inlet duct flow passage while in the third position,and at least a portion of the second door is not disposed within theinlet duct flow passage while in the fourth position.
 3. The inlet doorassembly of claim 1 further comprising: a link coupled to the actuator,the link having first and second ends each coupled to the first andsecond doors.
 4. The inlet door assembly in claim 3, further comprising:first and second joining rods each having first and second ends, whereinthe joining rod first ends are each coupled to the first and seconddoors, respectively, and the joining rod second ends are each coupled tothe link first and second ends, respectively.
 5. The inlet door assemblyof claim 3, wherein the actuator is coupled to the first joining rod. 6.The inlet door assembly of claim 1, wherein the first door is locatedforward of the second door.